The present invention relates generally to monitoring the content of liquid contamination tanks.
Microwave radiation systems have been utilized on-board marine vessels including naval ships for monitoring changes in level of a particular fluid product contained within holding tanks. Such a microwave radar system is described for example in an article entitled xe2x80x9cMeasuring Level With Radar Technologyxe2x80x9d, published in a magazine SENSORS, dated April 1993. Such a system involves reflection of a radar signal from the top of the liquid in the tank for reception by the radar antenna transmitting the signal and conversion thereof into output data on total volumetric content of the collected liquid in the tank. Current processes and equipment involving radar type tank level indicating systems cannot differentiate between differing liquids within one tank, such as fuel and water or a mixture of two liquids forming a slurry interface. Shipboard fuel quality operations now usually dictate stripping of settled contaminants from the lowest point in a fuel storage tank, from which the contaminants with water and sediment are directed to a holding tank. Once such holding tank is full, usable fuel is reclaimed therefrom through a series of filtration processes for economic and environmental purposes. Natural settling causes the water to settle lower than the fuel and is removed prior to fuel reclamation. Nevertheless, large amounts of fuel-water mixture is directed overboard to avoid admission of gross water during the fuel reclamation process. It is therefore an important object of the present invention to provide a modified form of the foregoing type of radar signal system for monitoring the collection of fuel and water mixture in a contamination tank, which will indicate the relative amount of gross free water of the mixture collected within the tank.
In accordance with the present invention, a contamination tank within which a mixture of fuel and gross free water is collected will be monitored by a microwave radar system involving generation and transmission of separate level indicating signals which are respectively reflected from the top surface of the liquid mixture in the tank and an interface between the fuel and the gross free water of such mixture. The interface signal reflection is effected by disposition of a floatation ball at the interface level in the collected mixture, within the sounding tube of the radar system through which both of the level indicating signals are transmitted and reflected respectively from the top tank surface level of the liquid and the interface ball location. Pursuant to the present invention, such reflected signals are mixed to provide an output from which the volumetric content of the gross free water collected in the tank in addition to the total collected liquid volume may be obtained.